1. Field of the Invention
The invention particularly concerns a method of adhesively edge-padding a stack of collated carbonless copy paper so that upon being fanned out, the stack spontaneously separates into individual sets, each of which is adhesively bonded together at one edge. The method can also be used for edge-padding a stack of ordinary paper that has been collated into sets. Both the resulting edge-padded stacks and the hot-melt adhesive used for the edge-padding are believed to be novel.
2. Description of the Related Art
U.S. Pat. No. 4,217,162 (Glanz et al.) says: "For many years carbonless copy paper has been made into form sets from a lift of collated sheets by applying an adhesive to one edge of the lift, drying the padded edge and fanning the lift into individual form sets. British Pat. No. 1,263,510 discloses an improvement in edge-padding performance by using as the adhesive a mixture of an aqueous solution of a gelatin derivative and an aqueous emulsion of a polymer. Further improvements in edge-padding are taught in U.S. Pat. Nos. 3,960,638; 3,963,533; 3,970,500; 3,970,501; and 4,041,193 where a naphthalene sulfonic acid-formaldehyde condensate is used in an edge-padding adhesive formulation in various combinations with materials such as water-soluble polymers, water-soluble binders, water-soluble metal salts, polymer emulsions, surface active agents and latexes. Japanese Pat. Publication Nos. 12844/1978 and 12845/1978 teach the use of a surface active agent with an aqueous solution of a synthetic polymeric adhesive, respectively, in an edge-padding adhesive formulation. Japanese Pat. Disclosure No. 99635/1974 teaches an aqueous edge-padding adhesive composition comprising a vinyl acetate/maleic acid copolymer and various alcohols" (col. 1, lines 19-43).
Like the adhesives mentioned in the foregoing quotation, the Glanz patent employs a water-based adhesive but says that better bonding within a set and better separation between sets is attained when the edge of the lift or stack is pretreated with water or certain aqueous solutions before applying the adhesive. One of the aqueous solutions that is said to be useful is a prior art edge-padding adhesive, namely an acrylic latex adhesive which apparently is used in all of the examples. The Glanz patent says: "Selective adherence occurs because the adhesive bonds the coated surfaces of the collated form, but not the uncoated surfaces" (col. 2, lines 29-31). Except for that statement, neither the Glanz patent nor any of the above-cited patents and publications explains why the adhesive adheres only to the coated surfaces.
Chem Abstracts, Vol. 99, Abstract 185057J (1983) reports that Japanese Pat. Application 81/160,004 (Fuchigami; also PCT Int. Application WO 83 01,228) uses an aqueous latex adhesive to bond the edge of a stack of carbonless or no-carbon paper that can be fanned apart into individual sets. The abstract says that "the outside surfaces of the copying paper set are coated with water resistant and/or water repellent substances to prevent adhesion between sets."
Several adhesives are currently marketed specifically for the purpose of edge-padding collated stacks of carbonless copy paper to be fanned into sets. These include "Fanapart High-strength Padding Adhesive" from Appleton Papers, Inc., Appleton, Wis.; "Mead Fan-Apart Adhesive" from the Fine Paper Division of Mead Paper Corp., Chillicothe, Ohio; "Nashua Expressway Fan-Apart Adhesive" from Nashua Corp; and "Fan-out Padding Adhesive" from 3M. Each of these is an aqueous adhesive, and the container of each instructs users to apply the adhesive by brushing, although it is understood that some users apply it by spraying and a few, by dipping. Brushing is usually done by hand, and considerable skill is required to attain a high degree of confidence that the edge-padded stack will separate correctly. Even if there were no failures, the brushing operation is messy and pollutes the atmosphere with materials that can have unpleasant odors. Spraying and dipping involve comparable problems.
In collated carbonless copy paper currently on the market, at least one of the outer faces of each set typically has been treated with a silicone or a fluorocarbon which counteracts curling that otherwise would result from the functional coating on the other surface of that sheet. That treatment also acts as a release agent for the edge-padding adhesive and can allow the adhesively edge-padded stack to separate into sets upon fanning, assuming that the edge-padding adhesive is not so thick as to create bridges that would inhibit such separation. Failures to separate are quite common.
The instructions on the Appleton container say that the stack can usually be fanned apart after 30 minutes and that complete drying and bonding occurs within two hours after applying. The Nashua instructions suggest drying for at least one hour before fanning. The only drying time in the Mead instructions is "at least three to four hours if sets include tag or ledger stock, or crash-imprinting is planned."
Sets of carbonless copy paper which have been edge-padded using aqueous adhesives are inevitably wrinkled at the adhesive bond and, when an individual sheet is removed, it always experiences some delamination at the adhesive edge.
3. Other Art
Hot-melt adhesives have been widely used to bind books, but the collated set of sheets that make up each book is always separated before the edge adhesive is applied. In U.S. Pat. No. 4,105,611 (Orth), after the sheets to be bound are stacked, a "weight bar contacts the sheets along a line which is spaced back a short distance from the sheet edges themselves, so that the edges are somewhat flared apart. Such flaring permits the adhesive to flow between the sheets for a short distance" (col. 2, lines 31-35). The hot melt adhesive of the Orth patent is comprised of, by weight, 30-40% ethylene/vinyl acetate (EVA) copolymer, 25-35% wax (preferably a paraffin wax), 20-40% of a modified rosin, and 10-30% of a fluid tackifier. Both of the latter two are considered to be tackifying resins.
West German Offenlegungsschrift DE 3,501,594 A1 (Koller; laid open Jul. 24, 1986) binds books with an EVA copolymer compounded with a tackifying resin and preferably also with either ethylene/butyl acrylate copolymer or a polyolefin. See also U.K. Pat. Application GB 2,167,074A (Tizzard et al.; printed May 21, 1986), the book binding adhesive of which likewise is primarily a mixture of segmented EVA copolymer and tackifying resin and may include waxes, e.g., petroleum waxes such as paraffin or microcrystalline waxes.
For a detailed discussion of adhesives based on EVA copolymers, see U.S. Pat. No. 4,497,941 (Aliani et al.) that says: "Conventionally, a hot melt coating formulation contains a polymer, a resin and a wax, a typical composition comprising 25% EVA, 25% resin and 50% wax" (col 6, lines 35-38). Aliani says that the wax "is present to reduce viscosity" and "also acts as an extender and a wetting agent and in some compositions as a set time improver" (col. 1, lines 41-46). Aliani avoids the wax by employing a new EVA copolymer involving the incorporation of a "chain transfer agent into the EVA copolymer. For example, when isobutylene is employed the product will be effectively an ethylene/vinyl acetate/isobutylene terpolymer. As used herein, the terms `EVA`, `EVA copolymer` and `ethylene vinyl acetate copolymer` include polymers containing such additional comonomers" (col. 8, lines 21-28). Aliani also describes a large number of prior EVA-based hot-melt adhesives that do employ wax.